Compute Sunrise, Sunset & Twilight For Cities & Airports Worldwide With Local TZ

This Sunrise/Sunset Computer is provided as a public service by
Fly-By-Day Consulting, Inc. and CompuSolve, Inc. and Leslie O'Shaughnessy Studios

Follow the steps below to compute sunrise/sunset.


Step 1 - Enter your location

In this step, you specify a point on the Earth for which the sunrise/sunset times will be calculated.

There are eight different ways we interpret the information entered in the box below; check off the box to tell us which way you are entering the location. Checking the correct box is important.

By Airport Airport ID
Specify a 3- or 4-letter designator for a U.S. or International Airport. Capitalization is not important. (Both IATA [Luggage tags] and ICAO [Flight planning & navigation] codes are known for most airports worldwide.)

Airport name
Several names are stored for some airports. If an exact match cannot be found then the closest match will be used, where "close" means exact except "Muni" instead of "Int'l", "Field" instead of "Executive", etc.

Return airport ID list for all airport IDs in that state or country that you enter. (Sometimes times out on some countries with many airports, such as Canada.)

By Name City, US State
City and US state, separated with a comma. The State is optional. Use the two-letter abbreviation for US states. Presently the only Cities known are those with airports. Some small airports may not be known.

Note: if the State is entered, it MUST be preceded with a comma (,).

City, non-US Country
City and Country, separated with a comma. The Country is optional. Use the full name of non-US country. Presently the only Cities known are those with airports. Some small airports may not be known.

Note: if the Country is entered, it MUST be preceded with a comma (,).

Note: there is only one database so if only a City is specified the first match completes the search. US data appears first.

County, State
Select County (for U.S. airports) optionally followed by U.S. state (using postal abbreviation) with a separating comma.

Note: a County is a political subdivision smaller than a State.

By Latitude/Longitude

Enter latitude as offset from the Equator
Enter as N42-44 W071-35 or S42.74 E071.6
If you do not know the latitude and longitude of the location that you are interested in, here's a link to an external Lat/Lon database by city. (Press the back button after you get the desired lat/long, and fill it in below.)

Enter latitude referenced from the South Pole
Enter as +132-44 +071-35 or +42.74 -071.6
Do NOT use this box for entering the latitude with a N or S in front of it.

Desired location, leave blank for Hollis, NH:

Notes for Location Entry

Countries other than the United States
Only the airport ID (designator), the city, and the country generally are known. (For most airports both ICAO and IATA IDs are known.)

Republic of and similar are removed when they are not universally used.

The word Island or Islands usually is retained when commonly used and should not be abbreviated. Sometimes Island and Islands have been accidentally swapped in the database.

The words Saint and Sainte usually is abbreviated as St or Ste or St. or Ste. but sometimes is spelled out. Most combinations are recognized.

Fort frequently is abbreviated as Ft or Ft., depending on local custom. Most combinations are recognized.

Compass directions that are parts of names should be spelled out.

The United Kingdom
Either England or Great Britain may be specified. Scotland, Ireland, Northern Ireland, etc. are listed as countries. Both Virgin Islands and British Virgin Islands are recognized.
USSR
There isn't one. Try Russia, Latvia, etc.
Islands
Most island countries are listed as themselves without any current or former colonial owner. This decision is on the basis of less typing and more likely matching rather than any political opinion.
India
Some of the cities in India that are known by the British names are being changed to the name used prior to colonial times. We store both names when they are known. Please inform us of any changes at bob@cavu.com.

Note: enter only one type of data, i.e., DeKalb/Peachtree or Atlanta, GA. Entering PDK DeKalb/Peachtree Atlanta, GA will fail.

Note: if you enter US State or non-US Country you MUST put a comma before it.


Step 2 - The date

Enter the date for which you wish to have the sunrise/sunset calculated.

Specify as Month and Day and, optionally, the year, e.g. Jan 15. Numeric and abbreviated months are allowed. The Month and Day must be included.

Spaces, slashes, or dashes should separate components. Do not enter extraneous characters. Years will assumed to be between 1951 and 2009; only the last two digits are needed. The year defaults to the current year.

It understands today, tomorrow, and yesterday (if time zone is correct). It also understands week as a week from today, and +x and -x as being x days from today. Defaults to today, of course.

Date (usually Month Day Year):

Note: if you select one of the (Europe) Output date formats in Step 4 then you must enter the Day before the Month here.

Note: if you request a table of data for multiple days then specify the date for the first day in the table, e.g., Feb 14.


Step 3 - Time Zone

Enter the time zone for the returned results.

Time zone: Automatic Eastern Central Mountain/Other Pacific/West Zulu/GMT
Custom time zone:

Will try to guess the location's time zone if Automatic is selected.

If there are several time zones for the state or country that sunrise and sunset are to be computed for and Automatic returned the wrong one (it defaults to Eastern) then try selecting Central, Pacific/West, or Mountain/Other in order. Note that the current local time is computed and displayed. If this differs with reality then the selected time zone is incorrect.

A Custom time zone may entered. Modern UNIX time zone syntax is recognized. This includes (GMT+x or GMT-x, where x is hours west (+) or east (-) of GMT (England). Alternatively, it may be ABCxDEF, where ABC are any letters displayed for standard (winter) time and DEF are displayed if summer time, and x is described above. US daylight saving time (summer time) rules will be used in this case.

Note: in some cases US or European rules for when to be on daylight saving time (summer time) will be used inappropriately for other countries. This means that he day that the switch to and from daylight saving time (summer time) may be off by up to three weeks for some countries; please report errors for correction.

You also can use the Custom time zone box to have the sunrise/sunset times for some other place given in your time zone. For example, if you are in the US Eastern time zone specify US/Eastern as the Custom time zone. (Note that this is one of the time zones listed below.)

If Custom time zone is specified then the other time zone buttons are ignored.

Custom time zone may also be any of the following:

WET CET EET GB-Eire

US/Alaska           US/Central       US/Hawaii       US/Pacific
US/Aleutian         US/East-Indiana  US/Michigan     US/Pacific-New
US/Arizona          US/Eastern       US/Mountain     US/Samoa

Canada/Atlantic     Canada/East-Saskatchewan    Canada/Mountain
Canada/Pacific      Canada/Central              Canada/Eastern
Canada/Newfoundland                             Canada/Yukon

Australia/LHI       Australia/North             Australia/South
Australia/Victoria                              Australia/Yancowinna
Australia/NSW       Australia/Queensland
Australia/Tasmania                              Australia/West

Step 4 - Control of Results

This section allows you to modify the presentation of the returned results.
How Long:
If, instead of a single day's data you would like a table of data for multiple days, suitable for printing, then make a selection below:
One day only
Daily for: 1 month 2 months 3 months 6 months 1 year (sometimes times out)

Miscellaneous:
Include beginning and end of Civil Twilight, for aviators.
Include Astronomical and Nautical Dawn and Dusk.
Include time of Midday
Include length of day (SR to SS)
Tables start on first of the month

Include accumulated lengths of days in month
Include accumulated lengths of days
Text color: White Black Background keyed to time of day (hard to see on some systems; may not print)

Output date format:
April 25, 1996
25 April 1996 (Europe)
04/25/96
25/04/96 (Europe)

Note: if you select one of the (Europe) Output date formats here then you must enter the Day before the Month in Step 2 when you specify the date.


Step 5

Get ready to compute!

Before you go, remember that we have a shortcut form for experienced users.

More notes on interpreting the results appear below!

Finally - press the button!


Strangeness near the North and South Poles

During the summer, latitudes near the North Pole are in perpetual sunlight (in varying degrees) and latitudes near the South Pole are in perpetual darkness. During the winter, conditions are reversed.

Therefore, at these high latitudes some events are listed as Does not occur. Since the various events (sunset, end of civil twilight, etc.) are officially defined as when the sun is at various positions in the sky, it is possible for some of these events to occur and some not to. (The sun may dip down enough for sunset but not for the end of civil twilight.)

If the sun "just barely" rises on a given day it might have shifted just enough to "just barely not" set that day, and likewise for other "mirror image" events. It is also possible for rounding errors to cause one and not the other to be listed. (You can try a date 15 days before and after to verify these.)


Definitions of Astronomical events

Sunrise/Sunset is defined as the instant in the morning/evening under ideal meteorological conditions, with standard refraction of the sun's rays, when the upper edge of the sun's disk is coincident with an ideal horizon.

Beginning/Ending of civil twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of six degrees (6) below an ideal horizon. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, the illumination is such that large objects may be seen but no detail is discernible. The brightest stars and planets can be seen and for navigation purposes at sea, the sea horizon is clearly defined.

The brightest stars and planets can be seen and for navigation purposes at sea, the sea horizon is clearly defined.

Beginning/Ending of nautical twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of twelve degrees (12) below an ideal horizon. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, it is dark for normal practical purposes. For navigation purposes at sea, the sea horizon is not normally visible.

Beginning/Ending of astronomical twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of eighteen degrees (18) below an ideal horizon. At this time the illumination due to scattered light from the sun is less than that from starlight and other natural light sources in the sky.

An ideal horizon exists when the surface forming the horizon is at a right angle to the vertical line passing through the observer's position on the earth. If the terrain surrounding the observer was flat and all at the same height above sea level, the horizon seen by the observer standing on the earth would approximate the ideal horizon.

The zenith distance is a vertical angle measured from directly overhead, down to the required point. An ideal horizon has a zenith distance of 90 degrees.

The vertical angle is the angle measured in a vertical plane, from the horizon to the required point. Directly overhead would have a vertical angle of 90 degrees.


The portion of the C code that computes events from a specified Latitude and Longitude was written by Arlin B. Collins (arlin@tarleton.edu) from articles in the April 1984 and July 1984 issues of Astronomy Magazine.
URL: http://www.compsolv.com/los/sunset.html
Maintained by bob@cavu.com
Last updated on 22 Feb 1999
Return to Home Page.